The Medical Research Council (MRC) has conducted two retrospective studies of prognostic factors in metastatic non-seminomatous germ cell tumours among patients treated in its participating institutions. In the first study, of 458 patients treated between 1976 and 1982, adverse features identified were (1) increasing tumour volume and (2) alpha fetoprotein (AFP) > 500 kU/l, or human chorionic gonadotrophin (HCG) > 1,000 IU/l. In the second study of 795 patients treated between 1982 and 1986, four adverse features were identified. These were (1) liver, bone or brain metastases, (2) AFP > or = 1000 kU/l or HCG > or = 10,000 IU/l, (3) mediastinal mass > 5 cm in diameter and (4) > or = 20 lung metastases. Using this data, two prognostic groups were identified and formed the basis of current multicentre randomised trials.